1. Field of the Invention
This invention relates to electric power-generating devices such as wind turbines and ocean current turbines, and more particularly to a method and apparatus for distributing to various gearboxes the input torque characteristic of low rotational velocity high-torque operation of wind or water turbine blades.
2. Description of the Prior Art
Many electric power-generating devices, such as wind turbines and ocean current turbines, benefit from economies of scale, yielding lower costs for generated electricity with larger power generation per unit. This increase in power is often accompanied by a reduction in rotational velocity of the power input shaft, resulting in a large increase in torque. Because electric generators require rotational velocities tens to hundreds of times greater than the rotational velocity of the input shaft, a speed increasing gearbox is often applied between the power input shaft and the generator. Generally, torque (.tau.) delivered by the power input shaft to the speed-increasing gearbox for such applications is given by EQU .tau.=P/.omega. (1)
where P is the power and .omega. is the rotational velocity of the power input shaft. Costs of conventional gearboxes (planetary, helical, etc.) increase exponentially with increased torque, diminishing the beneficial effects of increased scale. In addition, such high torque gearboxes must generally be custom designed and manufactured for specific application, further increasing their costs.
It is desirable to provide a way of reducing the torque on gearboxes resulting from slow moving turbine blades.
Prior art shows several inventions with multiple motors driving a single power output shaft, an application significantly different than the present application. Electric generating systems have been shown in the art to use multiple generators powered by a single gearbox. In each invention, the division of this power generating capacity to the multiple generators is done for power quality considerations. Division of gearboxes is becoming rare in recent commercial applications, largely because the cost of many small generators often exceeds the cost of a single large generator with the same capacity.
In addition, as turbines grow in size, the size and weight of individual components grow as well. Wind turbines place these components on top of a tower, presently stretching to over 60 m above the ground, while ocean current turbines are located at sea, where they can only be accessed by boat. The size of the components necessitates very large lifting equipment, making both the land-based cranes and ocean lifting equipment extremely costly. It is desirable to provide a way of reducing the weight and size of individual components of electricity generating equipment.
By dividing the powertrain into smaller components, generating systems receive an element of redundancy. For example, when ten small gearboxes and generators split the system's load, if one gearbox or generator experiences a fault, the system's capacity may only be reduced by 10%, allowing the system to remain active. A single set of components loses all of its capacity when a single component experiences a fault. It is desirable to provide a way of establishing reliability through redundancy in generating systems.